Unbleachable absorbance

The resist pattern was triangular, which was probably due to phenyl silane unbleachable absorbance. 

Two interesting attempts to redesign these resist materials have been reported. The first consisted of altering the structure of the sensitizer such that it bleaches in the DUV (70). The resulting resist provided adequate sensitivity but suffered from sensitizer volatility and solubility problems and profile degradation was experienced in films over 0.5 jiim micron thickness due to the unbleachable absorbance of the matrix resin from which the resist was formulated. 

Two-Component Resists. Typical two-component DNQ-novolac photoresists are not well suited for use in the deep UV because of the strong unbleachable absorbance of the novolac and sensitizer photoproducts below 300 nm. Therefore, the optical density of these materials is very high in the deep-UV and it does not decrease (bleach) with exposure. At doses that allow light to penetrate to the bottom of the resist, the top of the film is overexposed, and sloped profiles are produced. 

The synthesis and characterization of a novel class of diazoketones that function in a manner analogous to the diazoquinones but have bleachable absorbance maxima in the DUV region have been described (Figure 2.9). These systems are reported to function with photosensitivity comparable to that of the DQN systems, but their utihty still appears to be limited by the feet that they are employed in conjuction with a novolac resin, which has a substantial, unbleachable absorbance in the DUV region. This undesirable resin absorbance leads to reduced contrast 24, 25). 

Figure 2.9. The N-alkyldiazopiperidinedione structure is typical of the 1,3-diacyl-2-diazo compounds studied at IBM. Photolysis produces a carboxylic acid analogous to the chemistry of diazonaphthoquinones. These materials absorb strongly in the DUV region, but bleach completely as indicated in the spectra of a methanolic solution bottom). Resists formulated from these materials in novolac show residual unbleachable absorbance due to the resin as shown in the spectra of thin films (top).

The phenolic resins used in most of the commercial resists have a significant unbleachable absorbance at 313 nm but are essentially transparent above 350 nm. 

Bleaching is defined as any process that chemically alters pulp to increase its brightness. Bleached pulps create papers that are whiter, brighter, softer, and more absorbent than unbleached pulps. Bleached pulps are used for white or light colored paper. Unbleached pulp is typically used to produce boxboard, linerboard, and grocery bags. Of the approximately 65.5 million T (72 million tons) of pulp (including recycled pulp) used in paper production in the U.S. in 2000, about 50% is for bleached pulp.1... 

Figure 47, SAMPLE generated profile simulations in AZ1350J resist exposed at 436 nm on an index matched substrate. The mask edge is at 0.75um on the horizontal scale. The unbleachable optical absorbance (A) was varied from the actual value at 436 nm, 0.08 to 0.43. The dose was adjusted to develop each case to dimension (l.5um space) at constant development time. As A increases, all other factors being constant, the dose required to open the line increases and the resist profile becomes...

FWAs can only improve whiteness effectively if the substrate does not absorb too strongly in their excitation and fluorescence range. Objects with a poor basis white, such as unbleached textiles or poorly cleaned articles, cannot be brightened to a high degree of whiteness even with high concentrations of FWAs [119],... 

The resin matrix of dental materials has important influence on the chemical and physical properties of light cure resins. The organic formulations also include photoiniti-ating systems that absorb light. From there free radicals start the conversion of the oligomer blend to a polymeric cross-linked network. Camphorquinone (CQ) is widely used in dental resin mixed with an amine. However, CQ is a solid, yellow compound with an unbleachable chromophore. 

Figure 2.7 Relationship between amount of absorbed moisture by cellulose fibers and the relative air humidity (Kraft unbleached pine fibers).

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